Apparatus for automatically harvesting and then grading and sorting articles of agricultural produce are known in the art. Such apparatus generally is comprised of means for digging or gathering the articles of produce, such as potatoes or tomatoes, for example, and placing them on a moving endless conveyor. Means are provided for separating the articles from the vines or plants on which they grow and for separating from the produce other foreign matter such as rocks and clods of dirt.
In known potato harvesters, in particular, the apparatus is unable to successfully separate all rocks and clods of dirt from the harvested potatoes. Therefore, the potatoes with the undesired rocks and clods are conveyed to another conveyor which singulates the potatoes and foreign matter into a number of different rows. Each row moves past an inspection position where sources of radiation, such as light, illuminate the articles and foreign matter passing thereby. An optical system and photodetector means positioned above each of the rows of moving articles receives light reflected therefrom and produces two or more electrical signals which are functions of respective color components of light reflected from the articles of produce and from the foreign objects.
The grading of the articles of produce commonly is based upon a comparison and/or other operations on electrical signals which correspond to the color components in the light reflected into the optical system. The electronic apparatus which operates on the color signals is calibrated in such a manner that an eject signal is generated when an object other than a desired article of produce is in the field of view of the optical system. The eject signal actuates appropriate ejection mechanism such as a pneumatic valve and nozzle which produce a blast of air to discharge the undesired object from the conveyor system or from the free fall path of the articles of produce as they are discharged from the the conveyor onto further handling apparatus. Grading and sorting systems of this general type are known and need not be further described.
In automatic potato graders and sorters there is a considerable quantity of dirt carried on the potatoes and on the conveyor. If the optical system and air blast ejection system are positioned close to each other the optical system becomes covered with dust and dirt to such an extent that the amount of light that gets through the optical system to photodetectors of the color detectors is substantially reduced. This reduced light transmission to the photodetectors results in faulty operation of the grading apparatus.
To minimize the problem of dust and dirt collecting on the optical system it is desirable to separate the optical system as far as possible from the ejecting air blast where much of the dust is raised. This means, however, that the air blast ejector cannot immediately be actuated when an undesired article is first detected by the color grader apparatus since the air blast nozzle is physically displaced downstream from the location of the optical system. To account for this physical displacement it is possible to introduce a fixed time delay means in the electronic circuitry that actuates the valve of the air blast ejector. This has been used, but in systems where the articles of produce and the foreign objects are randomly positioned in respective rows on the conveyor, and where there is an appreciable variation in the sizes and shapes of objects to be ejected, it is necessary to have a rather long duration blast of air to assure that the blast will be fully effective on the object to assure its ejection. This practice consumes a large quantity of compressed air and requires a large compressor and large pressure tank. On mobile harvesting equipment the capacity of the source of electrical power to operate the compressor usually is limited, as is the physical space to house the compressor and pressure tank.